It's a normal good

BBC:

Last year, Newsbeat discovered that sex addiction was a growing problem among men in the UK.

80% of the sex therapists we contacted said an increasing number of males were asking for help with sex addiction.
...
Their behaviour can vary from compulsively watching porn online to visiting prostitutes at every opportunity.

And, yet, the demand for sex is not impervious to economic conditions:

Big Sister is not the only brothel suffering the effects of a battered global economy. While the world’s oldest profession may also be one of its most recession-proof businesses, brothel owners in Europe and the United States say the global financial crisis is hurting a once lucrative industry.

Egbert Krumeich, the manager of Artemis, Berlin’s largest brothel, said that in November, usually peak season for the sex trade, revenues were down by 20 percent. In Reno, Nev., the famed Mustang Ranch recently laid off 30 percent of its staff, citing a decline in high-spending clients.

But there are also supply effects, and demand substitution effects:

Hana Malinova, director of Bliss Without Risk, a prostitution outreach group, said she feared the current credit crunch was pushing more poor women into prostitution, since they could make more money selling their bodies — about 120 euros for a half-hour session at some upscale sex clubs in Prague — than flipping burgers at McDonald’s.

Even with the downturn, she added, prostitution was far more resilient than other industries, though the downturn was discouraging adultery. "... the recession is helping to keep husbands at home who might otherwise be cheating on their wives.”

Hmmm. Income down, sex with spouse up? Inferior good?